The present invention relates to securing a dangerous space or area, especially dangerous zones in the vicinity of automatically working machines.
Published German patent application DE 199 38 639 A1 discloses a system for securing a dangerous zone, especially one at an automatically working machine. The system employs first means for generating an optically monitored, virtual barrier, as well as second means for generating a switching signal to stop the machine when the barrier is breached. This system is characterized in that the first means employ a picture-taking unit as well as a defined target, the picture of which is taken by the picture-taking unit. The second means is a comparator which compares the taken picture with a characteristic value of a reference picture. In one embodiment, the first means also includes a light source for illuminating the target.
This system has significant disadvantages. The various components of this known system, such as the picture-taking unit and the defined target, are arranged independent of each other and must be separately aligned. For that, the independently defined target must be within the field of view of the picture-taking unit. Following the rough alignment of the picture-taking unit, in order to include the defined target, costly further alignment and processing is necessary. To take adequate pictures, the picture-taking unit further requires a large field of view. For this, the picture sensor requires a large, two-dimensional receiving surface.
This known system has the further disadvantage that it attains the required redundancy by duplicating the system to assure that the picture-taking unit and the defined target operate properly at all times to adequately protect the danger zone that is being monitored. This greatly increases the costs of such systems.
In addition, this known system cannot have a defined target in the area of the picture-taking unit and the light source. As a result, dead zones are formed in these areas which cannot be monitored and which therefore constitute unprotected portions of the danger zone.